1. Field of the Invention
The present invention relates to a pulley having plural fillets for preventing a belt used for power transmission from slipping off the pulley.
2. Brief Description of the Prior Art
FIGS. 3 and 4 show an example of conventional pulleys whose members are made of sintered materials such as sintered steel, copper and the like. Reference numeral 10 denotes a conventional pulley which includes a ring-shaped rim 11, a disc-shaped hub 12 and five arms 13 for connecting the rim 11 with the hub 12 so as to be coaxial therewith. The rim 11 includes an outer peripheral surface 14 having plural fillets 15 circumferentially disposed thereon at equal angular intervals about an axis of the rim 11. An inner cylindrical surface 16 of the rim 11 has a ring-shaped ridge portion 17 circumferentially disposed on the central portion thereof so as to project radially inwardly, the ridge portion 17 being smaller in thickness than the width of the rim 11 represented by character W as shown in FIG. 4 so as to divide the inner surface 16 into two parts, or first and second inner surfaces 16a and 16b. Each of the fillets 15 on the outer surface 14 extends parallel to the axis of the rim 11 and its top land 15a forms a plain surface together with the outer surface 14 of the rim 11. The hub 12 has an aperture 18 of a circular cross section disposed at the center thereof so as to be coaxial therewith, the aperture 18 being adapted for insertion of a rotatable shaft (not shown) for power transmission. Each of the arms 13 extends radially outwardly from a peripheral portion of the hub 12 to the ridge portion 17 of the rim 11 at equal angular intervals about an axis of the hub 12 or the axis of the rim 11.
Such a conventional pulley 10, used for power transmission in automobiles, is required to rotate silently at high speed, and therefore has been made from sintered materials which have a mechanical strength sufficient to endure those conditions. However, because sintered materials are expensive, the amount of material used to form the pulley 10 is preferably kept to a minimum.
Also, when the center of gravity of the pulley 10 is off-center, the pulley 10 rotates eccentrically and tends to vibrate and create noise. In this case, the problem can be resolved by lightening the weight of the pulley 10. Heretofore, the thickness of the rim 11 represented by character T as shown in FIG. 4, i.e., the distance of the inner surface 16 of the rim 11 to the top land 15a of the fillet 15, is made small. However, the thickness of the rim 11 represented by character t as illustrated in FIG. 3, i.e., the distance of the inner surface 16 to a bottom land 15b of the space defined between adjacent fillets 15 cannot be made smaller than the thickness necessary to provide sufficient mechanical strength to transmit power. Therefore, the pulley 10 requires some improvement to adequately transmit power in automobiles.